Engine crankshaft torque is an important factor in engine and vehicle performance. Fuel economy, drivability and operational smoothness in a vehicle driven by an automatic transmission are functions of transmission shift points and engine control parameters. Crankshaft torque is taken into account in order to optimize these shift points. The design and proper function of the drive train also must take into account crankshaft torque.
Crankshaft torque has been typically measured in test cells using highly specialized expensive dynamometer equipment and setups. The equipment, however, is large and very sensitive, making it totally unsuitable for vehicular applications.
Also, other attempts to measure engine crankshaft torque were made by machining "flats" into the engine crankshaft and installing stress or strain gauges onto the flats. As torque load is applied to the crankshaft, the strain gauges sense the induced stress load at their locations on the flats. The resulting signals from the strain gauges are compared with the torque calibration data, from which the torque values are inferred.
Such torque measuring devices are plagued by several problems. Life limiting modifications to the engine crankshaft are required for their installation, in addition to the difficulties and impracticalities of having to install sensors and physically load and calibrate each individual crankshaft, thereby disqualifying their use in commercial production vehicles. They also suffer from inaccuracy due to their inability to distinguish between stresses caused by torsional loads and stresses caused by non-torsional loads (i.e., axial loads, shear/radial loads, bending loads, or skew/misalignment loads).
The size constraints and accuracy problems inherent in prior art torque measuring devices (especially those utilizing slip rings) have greatly contributed to a resulting design cycle for the automobile drive train that is longer than the design cycle typical of the other primary automotive systems. The installation disadvantages of prior art torque measurement devices have also effectively precluded their incorporation into commercial production vehicles.